dhcp.c

   1 /*
   2  *   Copyright (C) 2010 Felix Fietkau <nbd@openwrt.org>
   3  *
   4  *   This program is free software; you can redistribute it and/or modify
   5  *   it under the terms of the GNU General Public License v2 as published by
   6  *   the Free Software Foundation.
   7  *
   8  *   This program is distributed in the hope that it will be useful,
   9  *   but WITHOUT ANY WARRANTY; without even the implied warranty of
  10  *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  11  *   GNU General Public License for more details.
  12  *
  13  *   You should have received a copy of the GNU General Public License
  14  *   along with this program; if not, write to the Free Software
  15  *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
  16  */
  17
  18 #include <sys/socket.h>
  19 #include <stdio.h>
  20 #include <string.h>
  21 #include <errno.h>
  22 #include <unistd.h>
  23 #include <fcntl.h>
  24
  25 #include "relayd.h"
  26
  27 struct ip_packet {
  28         struct ether_header eth;
  29         struct iphdr iph;
  30 } __packed;
  31
  32
  33 enum {
  34         DHCP_OPTION_ROUTER = 0x03,
  35         DHCP_OPTION_ROUTES = 0x79,
  36         DHCP_OPTION_END = 0xff,
  37 };
  38
  39 struct dhcp_option {
  40         uint8_t code;
  41         uint8_t len;
  42         uint8_t data[];
  43 };
  44
  45 struct dhcp_header {
  46         uint8_t op, htype, hlen, hops;
  47         uint32_t xit;
  48         uint16_t secs, flags;
  49         struct in_addr ciaddr, yiaddr, siaddr, giaddr;
  50         unsigned char chaddr[16];
  51         unsigned char sname[64];
  52         unsigned char file[128];
  53         uint32_t cookie;
  54         uint8_t option_data[];
  55 } __packed;
  56
  57 static uint16_t
  58 chksum(uint16_t sum, const uint8_t *data, uint16_t len)
  59 {
  60         const uint8_t *last;
  61         uint16_t t;
  62
  63         last = data + len - 1;
  64
  65         while(data < last) {
  66                 t = (data[0] << 8) + data[1];
  67                 sum += t;
  68                 if(sum < t)
  69                         sum++;
  70                 data += 2;
  71         }
  72
  73         if(data == last) {
  74                 t = (data[0] << 8) + 0;
  75                 sum += t;
  76                 if(sum < t)
  77                         sum++;
  78         }
  79
  80         return sum;
  81 }
  82
  83 static void
  84 parse_dhcp_options(struct relayd_host *host, struct dhcp_header *dhcp, int len)
  85 {
  86         uint8_t *end = (uint8_t *) dhcp + len;
  87         struct dhcp_option *opt = (void *)dhcp->option_data;
  88         static const uint8_t dest[4] = { 0, 0, 0, 0 };
  89
  90         while((uint8_t *) opt < end) {
  91                 if ((uint8_t *) opt + opt->len > end)
  92                         break;
  93
  94                 opt = (void *) &opt->data[opt->len];
  95                 switch(opt->code) {
  96                 case DHCP_OPTION_ROUTER:
  97                         DPRINTF(2, "Found a DHCP router option, len=%d\n", opt->len);
  98                         if (!memcmp(opt->data, host->ipaddr, 4))
  99                                 relayd_add_host_route(host, dest, 0);
 100                         else
 101                                 relayd_add_pending_route(opt->data, dest, 0, 10000);
 102                         break;
 103                 case DHCP_OPTION_ROUTES:
 104                         DPRINTF(2, "Found a DHCP static routes option, len=%d\n", opt->len);
 105                         break;
 106                 case DHCP_OPTION_END:
 107                         opt = (void *) end;
 108                         continue;
 109                 default:
 110                         DPRINTF(3, "Skipping unknown DHCP option %02x\n", opt->code);
 111                         continue;
 112                 }
 113
 114         }
 115 }
 116
 117 bool relayd_handle_dhcp_packet(struct relayd_interface *rif, void *data, int len, bool forward)
 118 {
 119         struct ip_packet *pkt = data;
 120         struct udphdr *udp;
 121         struct dhcp_header *dhcp;
 122         struct relayd_host *host;
 123         int udplen;
 124         uint16_t sum;
 125
 126         if (pkt->eth.ether_type != htons(ETH_P_IP))
 127                 return false;
 128
 129         if (pkt->iph.version != 4)
 130                 return false;
 131
 132         if (pkt->iph.protocol != IPPROTO_UDP)
 133                 return false;
 134
 135         udp = (void *) ((char *) &pkt->iph + (pkt->iph.ihl << 2));
 136         dhcp = (void *) (udp + 1);
 137
 138         udplen = ntohs(udp->len);
 139         if (udplen > len - ((char *) udp - (char *) data))
 140                 return false;
 141
 142         if (udp->dest != htons(67) && udp->source != htons(67))
 143                 return false;
 144
 145         if (dhcp->op != 1 && dhcp->op != 2)
 146                 return false;
 147
 148         if (!forward)
 149                 return true;
 150
 151         if (dhcp->op == 2) {
 152                 host = relayd_refresh_host(rif, pkt->eth.ether_shost, (void *) &pkt->iph.saddr);
 153                 if (host)
 154                         parse_dhcp_options(host, dhcp, udplen - sizeof(struct udphdr));
 155         }
 156
 157         DPRINTF(2, "%s: handling DHCP %s\n", rif->ifname, (dhcp->op == 1 ? "request" : "response"));
 158
 159         dhcp->flags |= htons(DHCP_FLAG_BROADCAST);
 160
 161         udp->check = 0;
 162         sum = udplen + IPPROTO_UDP;
 163         sum = chksum(sum, (void *) &pkt->iph.saddr, 8);
 164         sum = chksum(sum, (void *) udp, udplen);
 165         if (sum == 0)
 166                 sum = 0xffff;
 167
 168         udp->check = htons(~sum);
 169
 170         relayd_forward_bcast_packet(rif, data, len);
 171
 172         return true;
 173 }
 174
 175